The Tree of Life: A Review of Visual Conventions in Ernst Haeckel’s “Pedigree of Man”

Visual language is pervasive in life and its design is intrinsically rhetorical. Wherever one encounters information, one is bound by the visual conventions, interpreting and deploying them with or without conscious recognition. Kostelnick and Hassett’s book Shaping Information: The Rhetoric of Visual Conventions approaches the study of visual language examines the visual conventions that emerge, develop and decline in the history of visual design from a historical perspective. The book has touched upon several key questions concerning visual conventions: firstly, what is considered as “visual convention” and where is the line between convention and invention? Secondly, what factors have shaped and transformed visual conventions? Thirdly, how people perceive and work with these conventions?

In answering and evaluating these questions, I would like to use Ernst Haeckel’s visualization of “The Tree of Life” as a telling example in relation to Kostelnick and Hassett’s book. The “Tree of Life” is actually a page from Ernst Haeckel’s book The Evolution of Man: a Popular Exposition of the Principal Points of Human Ontogeny and Phylogeny (1879), titled “Pedigree of Man”. Haeckel’s series of visualization derives from Charles Darwin’s metaphorical description of the pattern of universal common descent, namely, the theory of evolution.

Even with a brief look at this page, the adaptations and transformations that the designer has tried to make on the visual conventions of the tree patterns is obvious. The idea of evolution is made literal by adopting a branching tree (probably an old oak tree) as the background and structure of the whole presentation. The Tree of Life is not a novel concept. It is very pronounced in the cultural and intellectual history (such as the trees of wisdom and life in the Bible, the tree of Enlightenment in the Buddhist tradition, the branching tree metaphor in Charles Darwin’s evolution theory…). It is an interesting comparison between Haeckel’s tree and Darwin’s sketch in the notebook. Unlike Darwin, who uses simple lines for branches in the way that a scientist usually does, Haeckel designs a much more elaborate visualization with details and vividness in the tree. The structure of the tree from its crown to root signifies a hierarchy. “Man” is at the crown of the tree (and also in capital letters), below which are two diverging branches, marked as Gorilla and Orang. In this image, most of the creatures on earth are mapped out in this tree of life, from top to bottom, from Man to Monera (a traditional division in biology that contains unicellular organisms without a nucleus). For Ernst Haeckel, as for many early evolutionists, humans were considered the pinnacle of evolution and this belief is strongly embodied in his design of the Tree of Life. Haeckel’s design can be seen as a transportation of the visual convention of the natural hierarchy, which has been one of the major ideas that shape the visual representation during Middle Ages. The print “Great Chain of Being” from Didacus Valdes’ 1579 book Retorica Christiana is one of the benchmark of the visual convention of hierarchy, with God at the top of the image and each lowering level include angels, man, birds, animals and plants, all of which are depicted in detail and liveliness. Haeckel’s tree design transforms this visual convention of religious hierarchical order into the representation of a scientific belief.

With a closer examination of the page, one can pick up more details in the convention of formatting: this is an illustration accompanying a book. The title of the book is printed on the top-left, while the numbering of this illustration is on the top-right. The number is in Roman number “XV” instead of the Arabic number “15” to itemize the illustration. Such formatting conventions are still very much alive today. Furthermore, the choice of typography and the organization of the page register a sense of scholastic seriousness into the visualization. Below the header section, the title of this image is printed in upper case with a period. Squares are chosen to enclose the name of each species (all properly capitalized) in order to convey the information with clarity. Towards the left margin of the page, the designer uses braces to indicate the different category of the species, giving their names vertically in English, and Latin in brackets. The font Times New Roman is adopted throughout the page. Though the printing and publishing technology has improved significantly, contemporary scholarly publications have made few changes to these conventions and they have stayed rather stable.

Furthermore, I would like to compare Haeckel’s Tree of Life to a twenty-first-century representation. The computer and Internet technology has enabled this Interactive Tree Of Life, which is an online phylogenetic tree viewer. All the species are structured in a circle with branches spreading out. Users can click onto each branch to look up for a certain division as well as to trace back to its root, which locates closer to the center of the circle. Colors and legends for them are used to indicate different categories (Eukaryotes are colored red, archaea green and bacteria blue). Users can also individualize their own Tree of Life by editing descriptions and adding photos to the system. The Interactive Tree of Life has once again transformed the visual conventions and hardly resembles a real tree in appearance; however, it keeps the concept by using expressions such as “Add leaves to the tree” and “Trace back to tree root” for action buttons.

In a sense, visual conventions are “works-in-progress”, which endlessly transform, evolve, and distinct as much as the different species do in the natural history. The progress depends on many factors including the discourse community of the visual language, its rhetorical purpose, as well as the practical elements of technology. Such conventions can influence one’s perception, but also inspire inventions. They can also be highly related to the cultural and intellectual belief as the example of Ernst Haeckel’s image of “Tree of Life” shows.